EP0276513A1 - Intrusion detection and land vehicle identification device - Google Patents

Abstract

The device (201) comprises an optical system for focusing a narrow detection beam (203) of passive infrared radiation along a reference plane (U). A filter selects the spectral analysis band and at least one passive infrared detector is placed in the focal plane. The device also comprises a first system for analog processing and a second system for digital processing making it possible to reconstitute, according to a characteristic curve, at least the line of movement of vehicles. On this curve, each element turning off the line of movement assumes the form of an identifiable pulse. …<??>Application to identification of vehicles moving over a predetermined site. …<IMAGE>…

Description

The invention relates to a device for detecting intrusion and recognizing land vehicles when the latter cross a reference plane, comprising an optical system for focusing a narrow beam for detecting passive infrared radiation along said reference plane. , a filter for selecting the analysis spectral band and at least one detector placed in the focal plane of said optical system.

This device can have civil or military applications. It is essentially designed to identify the general shape of mobile vehicles, more precisely the proportions between some of their characteristic elements and not their speed or their direction of movement. This involves, for example, recognizing the nature of vehicles entering or leaving a parking lot or vehicles not authorized to circulate on certain tracks or within the confines of a factory, etc. The typical military application is that which, in association with other sensors or sensors, participate in the development of an automatic ignition order for an anti-tank trap. The principle of detection of objects, people or vehicles by passive infrared radiation detectors, pyroelectric detectors in particular is known and used for example to automatically trigger the opening of doors when a passive infrared radiation (IR-P) is emitted by the object in a narrow detection beam. Particularly known from European patent No. 0 065 159 is a motion detector for monitoring a space which uses infrared thermal radiation from an unauthorized person entering, and in which the radiation receiver is a pyroelectric element. Increasingly, infrared detectors Passive reds (IR-P) are preferred over Doppler radar devices which are much more prone to false alarms and which can be detected because of the electromagnetic radiation they emit, the latter characteristic being a drawback for military applications. Pyroelectric detectors are easy to use, due to the fact that they require no cooling, and are suitable for detection within a maximum radius of a few tens of meters beyond which the thermal noise of the detectors becomes preponderant compared to the wanted useful signal. . In the foregoing, this is a simple detection which provides no other information than that of the presence or absence of a hot object in a detection beam. In addition, infrared thermography systems are known which, by means of a thermal camera and a television monitor, make it possible to obtain an image by passive infrared radiation of a field of vision which can be distant by several kilometers and according to several tens of contrast levels. Such systems, which moreover always require cooling of the detectors, are complex and expensive.

The object of the invention is to implement, by means of passive infrared detector (s), the recognition of certain mobile vehicles by a simplified thermal imaging device.

This object is achieved thanks to the fact that the intrusion detection and vehicle recognition device defined in the first paragraph is remarkable in that each detector is followed by a first analog processing chain for signal amplification and filtering and in that it further comprises, after said first chain, a second digital signal processing chain comprising means for sampling, storage of samples and processing of samples in such a way that at least the train of rolling of said vehicles is reconstituted by so-called signal processing means in the form of a time-dependent curve according to which each rotating element of the undercarriage takes the form of an identifiable characteristic pulse.

The invention exploits the property that the rotating elements of the undercarriage of a vehicle have to heat up by friction and / or elastic deformation during the movement of this vehicle.

The speed of the vehicle or the angle at which it appears in relation to the reference plane influences the time it takes to cross the plane, that is to say on the scale of the abscissa of the curve. However, the proportions between relative spacings of the different characteristic pulses of the curve are preserved in this homotety. These proportions, above all, are representative of the shape of a particular vehicle, in conjunction with its size, which allows the desired identification.

Furthermore, the resolution in field of the detection beam is physically limited to a minimum value such that it could prove to be insufficient for vehicles of too small size, which makes it possible to exclude the latter, as well as people, from vehicle classes to be identified. In this regard, an advantageous embodiment of the device is remarkable in that at the maximum observation distance provided and for all the expected angles of presentation of said vehicles with respect to said reference plane, the opening in bearing of said beam of Passive infrared radiation is such that the distance between two adjacent rotating elements of the undercarriage is resolved by each detector.

For a fairly large surveillance zone, the device of the invention must be designed to operate in a window at a distance of between a few meters and a few tens of meters; under these conditions, an advantageous embodiment is remarkable in that it comprises a plurality of n pyroelectric detectors arranged vertically and adjacent to each other so as to define in the reference plane n adjacent detection sub-beams of respective site angle ϑ _{s / n} of the order of a few degrees , the angle of elevation ϑ _{s of} said beam being counted downwards from a horizontal of the reference plane located approximately 1 m in height.

Depending on the distance of the vehicle when it crosses the reference plane, its undercarriage is detected in one or more detection beams, which makes it possible both to detect the entire undercarriage and also to obtain a indication on the distance of the vehicle.

• La figure 1 représente de façon schématique vu de côté le dispositif selon l'invention mis en place sur un site prédéterminé.
• La figure 2a illustre une disposition constructive permettant de matérialiser la technique de détection en infra­rouge passif selon l'invention.
• La figure 2b est un schéma synoptique de la premiè­re chaîne de traitement analogique.
• La figure 3 montre la courbe obtenue pour un véhi­cule à pneus.
• La figure 4 montre la courbe obtenue pour un véhi­cule chenillé.
• La figure 5 illustre comment est déterminée l'ou­verture en gisement d'un détecteur.
• La figure 6 représente, selon une vue semblable à celle de la figure 1, le cas de plusieurs détecteurs pour une détection dans une porte en distance large.
• La figure 7 est un schéma synoptique de la deuxième chaîne de traitement numérique.

The description which follows, with reference to the appended drawings, all given by way of example, will make it clear how the invention can be implemented.

• Figure 1 shows schematically seen from the side the device according to the invention set up on a predetermined site.
• FIG. 2a illustrates a constructive arrangement making it possible to materialize the passive infrared detection technique according to the invention.
• Figure 2b is a block diagram of the first analog processing chain.
• Figure 3 shows the curve obtained for a tire vehicle.
• Figure 4 shows the curve obtained for a tracked vehicle.
• FIG. 5 illustrates how the opening of a detector is determined.
• FIG. 6 represents, in a view similar to that of FIG. 1, the case of several detectors for detection in a door in wide distance.
• Figure 7 is a block diagram of the second digital processing chain.

In FIG. 1 is shown a detection and monitoring device according to the invention, 201. This device is installed, fixed, on a site 202, and comprises, as shown in FIG. 2a, an optical system making it possible to focus , on at least one detector, a narrow beam for detecting passive infrared radiation (IR-P). The detection beam 203, seen transversely, comes from a point 02 located approximately 1 m high; its elevation angle ϑ _s of the order of one to several tens of degrees is limited by a substantially horizontal straight line 204 and an oblique 205 directed downwards and the axis of symmetry 206 due beam 203 is an oblique which meets the ground between a few meters and a few tens of meters. The bearing angle ϑ _g , not shown, is of the order of one to a few tenths of a degree.

A description is given below with reference to FIGS. 2a and 2b of the intrusion detection system carried out by the passive infrared sensor that the device 201 includes. The beam 203 is obtained from the following elements:
an optical system 208 characterized by its focal distance f, its opening and its optical axis 206,
- a network of IR-P detectors 209 placed in the focal plane of the optical system 208, constituted by an assembly of infrared detectors 211, 212, 213, 214, sensitive in the infrared analysis band used, the dimensions as well as the relative arrangements combined with the distance f of the optical system 208 give the field of analysis constituted by the detection beam 203. It will be noted on this subject that it is possible to use a single detector at 209. The detectors are preferably sensitive pyroelectric detectors in the electromagnetic radiation band between 1 µ and 15 µ wavelength. These are, for example, RPY94 or RPY98 detectors, the dimensions of which are approximately 1 mm × 2 mm, manufactured by the English company Mullard. A filter 210 makes it possible to select the spectral analysis band, for example between 3 μ and 14 μ, and preferably between 8 and 12 μ.

It will be noted that the beam 203 whose solid analysis angle is ϑ _s .ϑ _g consists, in the example of FIG. 2a, of n under contiguous beams in a vertical reference plane U gui comprises the axis 206 , opening in deposit: ϑ _g and opening in site ϑ _{s / n} , n being equal to 4 in the example chosen.

Each detector of the network 209 is followed by an analog signal processing chain shown in FIG. 2b. This chain comprises in cascade the detector 216 which represents one of the detectors 211, 212, 213 or 214, a preamplifier 217, an amplifier 218 and a bandpass filter 219. The filter 219 supplies the voltage V₂₁₆ (V₂₁₁, V₂₁₂, V₂₁₃ or V₂₁₄). The overall bandwidth of this processing chain is between a few tenths of Hz (typically 0.5 Hz), to be insensitive to the DC component, and a few tens of Hz (typically 50 Hz), which corresponds to the frequency of maximum modulation necessary to take into account vehicles likely to cross the reference plane U. The assembly constituted by the optical system 208, the filter 211, the detector 216 and its amplification and filtering chain has a temperature difference - noise equivalent (NETD) less than 1 ° K.

The purpose of the simplified infrared analysis carried out by the invention is to collect, day and night, a certain amount of information on one (or more) vehicle (s) having passed through the detection beam 203, either for identify, whether or not to place it in the class of objectives to be destroyed in the context of a military application. In the latter case, this analysis comes after certain tests relating to the passing distance and the vehicle speed have been successfully passed.

The criteria taken into consideration for the design of the device 201 are the following:
- Vehicles in the vicinity of the device will be mobile and will rarely appear from the front. The beam or the contiguous sub-beams, 203, although fixed, will take advantage of the movement of the vehicles to perform the longitudinal analysis of their sides.
- The vehicles which will reach the reference plane U will have driven for a long time, which will have resulted in overheating of their running gear, whether in the case of tracked vehicles or on tires.
- The position of the device 201, very close to the ground is such that the lower part of the vehicle body will remain in the beam 203 throughout the time of its travel, and this regardless of the angle ξ made by the trajectory of the vehicle (not shown) with the plane U, the angle ξ being assumed to be between 45 ° and 135 °.
- The detectors of the analysis beams will not be sensitive to the DC component, which has several consequences: on the one hand infrared phenomena with very slow evolution in the environment are not annoying, such as the sun for example. Furthermore, constant temperature zones on vehicles will not generate any signal, only counting the transitions. The running gear of vehicles is a characteristic attribute of these.

In the case of a vehicle on tires, see FIG. 3, the tires 221, 222 are heated by friction and deformation. These tires (typically three in number for a truck) are rarely hidden because at the front (221) the wheels provide direction and the necessary lateral movement prevents them from being fully integrated behind the bodywork and at the rear (222), for reasons of ease of access, they are not covered with a cover.

For a tracked vehicle, Figure 4, the rocker panel consists of a number of rollers 223 generally greater than 6. On these rollers rub the tracks 224, which has the consequence of bringing their periphery to an apparent temperature sensitive. These rollers are provided with a long-travel suspension, so they are not entirely maskable by skirts. In FIGS. 3 and 4, to facilitate the representation, a kinematic inversion has been produced according to which the virtual image of the detector is supposed to move, in the direction of an arrow 226, between the ground 202 and a horizontal plane PH passing through. by line 204 (Figure 1), along the lower part of the vehicle, the actual movement being opposite. This movement takes place on a linear scale. This results for the output signal V₂₁₆ of the analog processing chain, the curves c as a function of time 227 and 228. These curves consist of pulses 229, respectively 231, slightly hollowed out in their center and whose spacing ratios in time are the same as the linear spacing ratios of the rotating elements belonging to the undercarriage of the vehicles. Curves 227 and 228 are sampled and processed in digital form as described below with reference to FIG. 7.

The attributes exploitable from curves 227 and 228 are pulses (peaks) of sufficient amplitude to assimilate them to as many elements of the running gear. We can then count the number of pulses, their width, their spacing and make a comparison with typical curves representative of this or that class of vehicles.

It will be noted that the distance from the vehicle has no influence on the duration of crossing the reference plane U. The parameters which influence this duration are the speed of the vehicle and its angle of presentation ξ relative to the plane U. The distance plays on the other hand, a role as regards the definition of the bearing angle ϑ _g of the detection beam 203.

To correctly analyze the running gear in a distance range from a few meters to a few tens of meters, the values of ϑ _g and ϑ _s or ϑ _{s / n must} be chosen according to the following criteria:
- The opening in deposit ϑ _g (see figure 5), must be chosen such that at the maximum observation distance D _max (nominal distance in the case of a road to be monitored), and for all target presentation angles (45 ° <ξ <135 °), the shortest distance d _min between adjacent rotating elements of an undercarriage be resolved by the detector (s). For the pair of values: D _max = 75 m and d _min = 30 cm, for example, this leads to the value: ϑ _g ≃ 0.2 °.
- For the opening in site ϑ _s or ϑ _{s / n} , the calculation is based on the possibility of observing tires or rollers of a tracked vehicle as described above with reference to Figures 3 and 4.

If the vehicle to be recognized is supposed to be traveling on a road, a single detector 216 may suffice. On the other hand, for a window with a fairly wide distance of between a few meters and a few tens of meters, a plurality of n pyroelectric detectors will be used, for example 4 detectors giving birth to 4 contiguous detection beams 233, 234, 235, 236 of elevation angle ϑ _{s / 4} as shown in Figure 6. Thus, when the vehicle is at the minimum observation distance D _min , the undercarriage occupies the vertical field of the n (n = 4) detectors. On the other hand, when the vehicle is at the maximum observation distance D _max , the undercarriage is in the field of a single detector, the one which corresponds to the upper sub-beam, 236. This condition makes it possible to define the value of ϑ _{s / n} . It will be noted that this constructive arrangement makes it possible to obtain a first indication of the passage distance of a vehicle. For example, in FIG. 6, when 4 detectors are involved in the detection, the vehicle is located between 12 and 20 m from the device 201; for 3 detectors involved, between 20 and 29 m; for 2 detectors, between 29 and 57 m, and for 1 detector, between 57 and 75 m.

Pour un système de détection plus complexe incorporant d'au­tres senseurs, il peut se faire qu'on ait à disposition la distance D du véhicule ainsi que sa vitesse angulaire apparen­te dγ/dt ; dans ce cas, il vient :

Cette dernière méthode de calcul permet de faire en sorte que le nombre d'échantillons pris sur un véhicule de longueur fi­xée soit le même quelle que soit sa distance de passage.For the processing of the output signals from the detectors 216, the digital signal processing chain of FIG. 7 is preferably used. FIG. 7 is suitable for the case of several detectors in which the signals V₂₁₁ to V₂₁₄ are supplied to a multiplexer 238 followed by a sampler-blocker 329. The multiplexer 238 is intended to bring successively to a single coding channel the signals V unique to V₂₁₄. The control signal on a conductor 241 of the multiplexer comes from a management processor 242 which supervises the operation of the entire device. In the case of a single detector, the unique signal V₂₁₆ is supplied directly to the sampler-blocker 239 which, under the control of a sampling signal at the frequency f _EIR on a conductor 243 coming from the processor 242 , takes the analog value of the signal (or signals) V₂₁₆. The digital processing chain of FIG. 7 further comprises an analog-digital converter 244 and a memory for storing the digital values of the samples, 245. The data processing circuit constituted by the processor 242 and its associated program memory 246 applies the digital filtering and algorithms for extracting the characteristic attributes of vehicles. The sampling period T _EIR of the signals at 239 must be calculated such that it is lower than the duration of a pulse 229 on 231. T _EIR can be determined from the minimum distance resolution rh which is wishes to have on the vehicle, whatever its angle of presentation ξ in a predetermined range of values and the value of the maximum apparent speed v _max of the vehicle. The value of T _EIR is therefore deduced from the relation:

For a more complex detection system incorporating other sensors, it is possible to have available the distance D of the vehicle as well as its apparent angular speed dγ / dt; in this case, it comes:

This last calculation method makes it possible to ensure that the number of samples taken on a vehicle of fixed length is the same regardless of its passage distance.

We have seen that the classification of vehicles to be identified is based on a search for attributes characteristic of the undercarriage. This is done by applying a certain number of digital processing operations on the samples contained in the memory 245, and in particular the comparison of these samples with one or more thresholds, allowing the identification of the pulses 229 and 231. Before applying these treatments, the passing distance of a vehicle can be taken into account as follows:
- if the passage distance is small, the attributes sought at the level of the undercarriage will not appear at each V₂₁₁, V₂₁₂, V₂₁₃, V₂₁₄ signal but on their sum (the 4 detectors cover the undercarriage).
- as the passing distance becomes large, the attributes sought will only appear on the sum of three signals, then two, and finally on a single signal.

The management processor 242 is for example a microprocessor 6809 from the company Motorola and the algorithms necessary for its programming for the implementation of the invention are within the reach of those skilled in the art, in this case the average computer scientist .

It will be noted that the optical part of the device can be produced in transmission by means of optical elements of germanium for example, or in reflection by means of a concave reflecting mirror constituted by a molded form of plastic material coated with a thin layer. metallic.

Claims (5)

1. Device for intrusion detection and recognition of land vehicles when the latter cross a reference plane, comprising an optical system for focusing a narrow beam for detecting passive infrared radiation according to said reference plane, a filter making it possible to select the spectral analysis band and at least one detector placed in the focal plane of said optical system, characterized in that each detector is followed by a first analog processing chain for signal amplification and filtering and in that that it further comprises, following said first chain, a second digital signal processing chain comprising means for sampling, for storing samples and for processing samples so that at least the running gear of said vehicles is reconstituted by said signal processing means in the form of a time-dependent curve according to which each rotating element of the train n rolling takes the form of an identifiable characteristic pulse. 2. Intrusion detection and recognition device according to claim 1, characterized in that said sample processing means are constituted by a microprocessor. 3. Intrusion detection and recognition device according to claim 1 or 2, characterized in that the assembly constituted by said detector and said first analog processing chain has a bandwidth between a few tenths of Hertz and a few tens of Hertz and that said assembly plus said optical system have a temperature-noise equivalent difference of less than 1 ° K. 4. Intrusion detection and recognition device according to one of claims 1 to 3, characterized in that at the maximum observation distance provided and for all the expected angles of presentation of said vehicles relative to said reference plane , the opening in bearing of said beam of passive infrared radiation is such that the distance between two adjacent rotating elements of the undercarriage is resolved by each detector. 5. Device for intrusion detection and recognition in a window of distance between a few meters and a few tens of meters according to one of claims 1 to 4, characterized in that it comprises a plurality of n pyroelectric detectors arranged vertically and adjacent to each other so as to define in the reference plane n adjacent detection sub-beams of respective site angle ϑ _{s / n} of the order of a few degrees, the site angle ϑ _s of said beam being counted downwards from a horizontal of the reference plane situated approximately 1 m in height.

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